Electronic devices, such as cellular telephones, cameras, automobiles, and computers, commonly use image sensors to capture images. A typical CMOS (complementary metal-oxide-semiconductor) imager circuit includes a focal plane array of pixels, and each pixel includes a photo-sensor, such as a photogate or photodiode for accumulating photo-generated charge in a portion of the substrate.
Digital images are constructed using data from the pixels, and may be described according to their spatial resolution. Images having higher spatial resolution are composed with a greater number of pixels than those of lower spatial resolution. In general, there are trade-offs between the frame rate (the number of times the full pixel array can be read in a second), spatial resolution, and power consumption. To obtain high resolution images, conventional systems readout the entire pixel array, which results in lower frame rates and requires higher power consumption. To maintain the same frame rate, the systems that produce higher resolution images must consume more power relative to the systems that produce lower resolution images, as power consumption is related to the pixel clocking frequency.